TW200525304A - Enhancing photoresist performance using electric fields - Google Patents

Abstract

Electric fields may be advantageously used in various steps of photolithographic processes. For example, prior to the pre-exposure bake, photoresists that have been spun-on the wafer may be exposed to an electric field to orient aggregates or other components within the unexposed photoresist. By aligning these aggregates or other components with the electric field, line edge roughness may be reduced, for example in connection with 193 nanometer photoresist. Likewise, during exposure, electric fields may be applied through uniquely situated electrodes or using a radio frequency coil. In addition, electric fields may be applied at virtually any point in the photolithography process by depositing a conductive electrode, which is subsequently removed during development. Finally, electric fields may be applied during the developing process to improve line edge roughness.

Description

200525304 (1) IX. Description of the invention [Technical field to which the invention belongs] The present invention generally relates to the patterning of photoresist. [Prior Art] Photoresist can be used to transfer a pattern from a photomask to a semiconductor wafer in a repeatable pattern. Generally speaking, the lithography process involves the entire basic steps. Initially, a photoresist was formed on the top surface of the wafer by a spin coating process. Excess solvent is then removed during the pre-exposure baking process. After that, certain areas on the wafer are selectively exposed to radiation. Next, the wafer is baked in a so-called post-exposure bake. The wafer and especially the photoresist are then developed and cleaned. The exposed area may resist erasure or be more prone to erasure so that the pattern of a reticle is transferred to the wafer in a repeatable manner. The quality of the pattern transferred from the photoresist to the bottom layer is based at least in part on the so-called line edge roughness. The rougher the straight line transferred to the photoresist, the rougher the pattern transferred to the semiconductor wafer, which in turn will affect the performance of the device at the completion of manufacturing. Therefore, I intend to reduce the straight edge roughness of the photoresist. [Summary of the Invention] and [Embodiments] Referring now to FIG. 1, a semiconductor substrate 12, such as a wafer covered by a layer of other materials (such as a dielectric layer), is formed by an unexposed, undeveloped photoresist 1 0 is covered. The photoresist can be spin-coated on the substrate 12. In an embodiment of 2005-5-304 (2), the substrate 12 can be polished and the photoresist 10 can be exposed to an electric field labeled E. In one embodiment, an electric field is supplied before or during a pre-applied bake and can improve the distribution of the polymer in the photoresist. The photoresist 10 can be a 193 nm or an extreme ultraviolet (EUV) photoresist, which can be a mixture of two polymers and / or an arbitrary molecular polymer containing both polar and non-polar components. The photoresist 10 may be a hydrated polymer or an isomolecular polymer such as a poly (methacrylate) -based or polyhydroxystyrene maleic anhydride and an olefin-based block polymer. The 193 nm photoresist may have aggregates randomly distributed in the formed photoresist 10. These aggregates can cause line edge roughness in some embodiments. The aggregate can be formed right after the photoresist 10 is spin-coated on the semiconductor substrate 12 regardless of subsequent exposure and development procedures. In addition, the roughness of the photoresist 10 may be transferred to the underlying substrate 12 in a subsequent etching process. The aggregate may be denser than the photoresist 10 as a whole. The density of these aggregates can prevent them from fully developing after exposure by reducing acid diffusion / entry into the aggregates. One problem caused by these aggregates is their lateral and vertical extension. In detail, an extension in a direction parallel to the surface of the substrate 12 may cause line edge roughness in some cases. One possible cause for these aggregates is the hydrated structure between the polar portions of the polymer chains that make up the photoresist 10. Positioning the polar polymer chain element in a more vertical direction than the horizontal direction can reduce the line edge roughness -6-200525304 (3) degrees. By exposure to an electric field, the aggregate M 1 (Fig. 2) can become more aligned in a vertical direction, as shown in M2 of Fig. 3, and converge horizontally. As a result of this action on a large number of aggregates, molecules or elements of the photoresist, the line edge roughness can be reduced. When the photoresist 10 is above its glass transition temperature, the electric field may be applied before exposure and before or during pre-exposure baking. This can be achieved by heating the photoresistor 10 or by the solvent-induced suppression of the glass transition temperature. Exposure to the electric field E shown in FIG. 1 may involve expanding the photoresist 10 with a non-polar solvent. Once the photoresist 10 has been positioned by the electrical field, the solvent can be removed, such as by 'heating (pre-exposure baking) or other solvent removal techniques. This solvent removal can effectively "freeze" or cause permanent molecular vertical orientation. The orientation of the polymer may be generated during pre-baking or before pre-exposure baking. In one embodiment, two pre-exposure bakes may be used: an initial bake is to position the polymer, and a second bake is to remove the solvent. Positioned photoresist 10 with the solvent removed can be prepared for exposure and development in a conventional lithographic process. These techniques are particularly useful for 1 93 nm or EUV photoresist systems with aggregates. The voltage of the electric field E used to locate the polymer or bi-block heteroatomic polymer constituting the photoresist 10 may be about several tens of volts in one embodiment. The distance between the electrodes generating the electric field E may be about one micrometer in one embodiment, and a long range progression is formed in the photoresist 10. A photoresist is formed; a polymer film of about 〇 may be about 200 nanometers thick, and in one example has a polymer 7- 200525304 (4) matrix having about 107 to 108 V / m High electric field. For the reduction of the edge roughness of the 193 nanometer line, the degree of ordering is about 5-20 nanometers, for example. The voltage used to achieve this result may be approximately less than ten volts, but the distance between the electrode supplying the electric field and the photoresistor 10 may be approximately several millimeters, of which a 300 mm wafer is used to form the substrate 1 2 . Depending on the size of the wafer, higher voltages on the order of tens to hundreds of volts can be used to maintain an equivalent electric field. In some embodiments, the potential advantage of supplying an electric field during pre-exposure baking is to provide a photoacid generator that oscillates the potential more evenly in the photoresist, thereby reducing one of the line edge roughness source. In another embodiment, an electric field may be supplied during the exposure. During the exposure, in some embodiments, the electric field can enhance photon velocity by adding energy to a secondary electrode generated by the far ultraviolet rays, wherein the secondary electrode can react to photoacid generators (PAGs). Photoresists with inherently low line edge roughness can be accelerated to acceptable fast photon velocities when exposed to an electric field. During exposure, the energy added to a free electron depends on the strength of the supplied electric field and the distance traveled by the electron before it is re-adsorbed or scattered. For a 5 nanometer scattering distance and a 100 volt voltage supplied at a thickness of 100 nanometers, the extra energy is about 5 eV, which may be more than the original energy of the secondary electrons. According to Fig. 4, the chemically strengthened far-ultraviolet photoresist can be controlled using a voltage supplied from a voltage source 16. In this example, the substrate 12 may be covered by a photoresist layer] 0. A potential is supplied through the photoresist 10 during post-exposure baking, pre-exposure baking, or during exposure. In the example of Yi Shi 200525304 (5), the shape of the δ helium electrode 16 a may be ring-shaped to avoid using the electrode before exposure] 6 a will hinder the exposure radiation. After exposure to the far ultraviolet rays R, electrons e are released. Although the use of a DC potential 16 is described herein, an AC power source may be used. In another embodiment, as shown in FIG. 5, a thin layer of a conductive material 14 may be applied to the photoresist 10 to supply a potential. After exposure to the far ultraviolet rays R, electrons e are released. In one embodiment, the conductive material 14 may be deposited by, for example, spin coating. The conductive material 14 may include a water-soluble conductive organic material, for example, a functionalized polythiophene. The conductive material 14 may also include a conductive polymer, such as a sulfonate photoacid generator. In addition to the gunsulfonate, the conductive material 14 may also contain an acidic substance, such as an ammonium sulfonate. The spin-coated electrode material 14 can work with a conventional photoresist. In one embodiment, the conductive material 14 is water-soluble so that it can be washed away during the development stage. Next, referring to FIG. 6, passing the alternating current through a radio frequency (or other) coil I 6b can increase the photon speed by increasing energy to the secondary electron e generated by far ultraviolet rays. The coil 16b may include a required electric field without hindering the exposure of the photoresist 10. Therefore, the coil 16b can be used before, after or during exposure. Referring to FIG. 7, an electric field may be applied to the conductive layer 14 during post-exposure baking. If the layer is sufficiently thin, the layer 14 can also be used before or during exposure. Each low-energy RF coil] 6b or electrode 16a can supply a potential of -9-200525304 (6) to the photoresist without using a conductive material 14. The coil 16b or the electrode 16a can simplify field exposure during post-exposure baking or pre-exposure baking. Therefore, in one embodiment, the photoresist can be spin-coated and exposed. Then, a conductive material as shown in Figs. 5 and 7 can be spin-coated thereon. Post-exposure baking of the wafer can be accomplished by supplying a potential, as shown in Figures 6 and 8. After that, the exposed structure is developed and washed. Alternatively, a potential can be supplied during the exposure. In yet another approach, the potential can be applied during pre-exposure baking. This potential can be applied, for example, during exposure or pre-exposure using a radio frequency application field. In another embodiment, an electric field may assist during photoresist development. The removal of the exposed baked photoresist with a developer can be achieved by means of an electrochemical reaction. This reaction can occur between a negatively-charged alkaline developer material (such as TMAH) and a photoresist-forming polymer (e.g., a phenol-based compound with a bi-block polymer that can be removed by development). In the presence of an electric field, the local concentration of hydroxide ions of the developer is given by the Bozman distribution: p (z) = p 0 expfeZW (z) / KT] where P0 is at the top surface of the developer Ion concentration, e is the charge, ζ is the valence of the ion, 离子 (ζ) is the local potential, K is the Bozman constant, and T is the temperature. By increasing an external potential V (operating system), the local density changes to: ρ (ζ) = p 0 exp [eZW (z) + V (z) KT] -10- 200525304 (7) This makes the development The concentration of the agent is changed by the applied electric field. Now referring to FIG. 8, according to another embodiment of the present invention, once exposed and undeveloped wafer 10a is placed on the ground plane 12, and the developer is dispersed in the developing module 30 until a slurry is produced. Mission so far. A charged electrode 28 is then placed on top of the slurry mass and an electric field is applied between the charged electrode 28 and the ground plane 12. A DC electric field (from a DC potential 20) creates a potential gradient between the top and bottom of the photoresistor 26 positioned on the wafer 10a. The photoresist development reaction rate is higher at the bottom of the photoresist 26, resulting in a more vertical profile and further enhancing the resolution. When the ground is at a more positive potential, an AC potential from the source 22 It will attract negatively charged ions and alkaline developer solution closer to the bottom of the photoresist 26. When the charged electrode 28 is at a more positive potential, the AC potential will attract negatively charged ions to the top of the photoresist. This results in a more uniform distribution of developer ions, such as negatively charged ions, which eases the line edge roughness. Although the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate that many modifications and variations can be derived from these embodiments. The scope of the attached application patent covers such modifications and changes as fall within the spirit and scope of the present invention. [Brief description of the drawings] Fig. 1 is a schematic cross-sectional view of an embodiment of the present invention; Fig. 2 is a schematic diagram of an aggregate exposed to the electric field shown in Fig. -11-200525304 (8); 3 is a schematic diagram of the effect of the electric field on the aggregate shown in FIG. 2; FIG. 4 is a schematic diagram of another embodiment of the present invention; FIG. 5 is a schematic cross-sectional view of another embodiment of the present invention; 6 is a cross-sectional view of still another embodiment of the present invention; FIG. 7 is a cross-sectional view of still another embodiment of the present invention; and FIG. 8 is a main cross-sectional view of a device according to an embodiment of the present invention Explanation of symbols] 1 〇: photoresist 12: substrate 14 4: conductive material] 6: voltage source 16 a: electrode 16 b: coil 2 0: DC electric field 22: source 2 6: photoresist 2 8: electrode 3 〇 : Developing module E: Electric field R: Radiation-12- 200525304 (9) e: Electron m: Aggregate m2: Aggregate

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Claims (1)

200525304 十 X. Scope of patent application 1 · A method including: processing an unexposed photoresist with an electric field. 2. The method of claim 1 in the patent application range, wherein the processing step includes exposing the photoresist to an electric field to reduce the level of the aggregates formed in the photoresist. 3. The method according to item 1 of the patent application scope, wherein the processing step includes reducing the line edge roughness by exposing the photoresist to an electric field before exposing the photoresist to radiation. 4. The method of claim 1, wherein the step of processing the photoresist comprises exposing the photoresist to an electric field while the photoresist is above its glass transition temperature. 5. The method according to item 4 of the patent application scope, comprising heating the photoresist to cause the photoresist to exceed its glass transition temperature. 6. The method of claim 5 including applying a solvent-induced drop to cause the photoresist to exceed its glass transition temperature. 7. The method of claim 1, wherein processing the unexposed photoresist includes using an electrode to generate the electric field, and the electrode has an opening so that the photoresist can be exposed to radiation. 8. The method of claim 1, wherein the processing step includes depositing a conductive layer on the photoresist to supply an electric field to the photoresist. 9 · The method according to item 1 of the scope of patent application, wherein treating the unexposed photoresist with an electric field includes generating the electric field by passing an alternating current through a coil -14- 200525304 (2) 1 ο The method includes using a radio frequency coil. 1 1. A method comprising: forming a conductive layer on a photoresist; and exposing the photoresist to an electric field using the layer. 12. The method of claim 11 in the scope of patent application, comprising depositing the layer so that radiation can penetrate the layer. 1 3. The method of claim 11 in the patent application scope, comprising depositing a conductive material to form the layer, and removing the layer after the photoresist is developed. 1 4 The method of claim 11 in the scope of patent application, including spin-coating the conductive layer. 15. The method according to item 11 of the scope of patent application, wherein forming a conductive layer includes depositing a water-soluble conductive material as the conductive electrode. 16. A method comprising: treating a photoresist with an electric field formed by passing alternating current through a coil. 17 · The method of claim 16 in the scope of patent application, including configuring the coil so that the photoresist can be exposed to radiation. 18 · The method of claim 16 in the patent application scope, including exposing the photoresist to the electric field while the photoresist is exposed to radiation to transfer a pattern to the photoresist. 19 · The method of claim 16 in the scope of patent application, including the use of a radio frequency coil. 2 0 · A method comprising: exposing a photoresist to radiation; and -15-200525304 (3) exposing the photoresist to an electric field while exposing the photoresist to radiation. 2 1 The method of claim 20, including using an electrode to expose the photoresist to an electric field, the electrode having an opening to allow the radiation to pass through. 2 2 · The method of claim 20, including exposing the photoresist to radiation via an electrode, the electrode being thin enough to allow the radiation to pass through. 2 3. The method of claim 20 in the scope of patent application includes using an RF coil to cause an electric field to expose the photoresist to the electric field. 24. The method of claim 20, including exposing the photoresist to extreme ultraviolet radiation. 2 5 · A method comprising: forming a photoresist on a substrate; baking the photoresist before exposure; and applying an electric field while baking the photoresist. 26. The method according to item 25 of the patent application scope, including using an RF coil to expose the photoresist to an electric field. 27. The method of claim 25, including using an electrode having an opening therethrough to expose the photoresist to an electric field. 2 8 · The method according to item 27 of the scope of patent application, including the use of a ring electrode. 29. The method of claim 25, including exposing the baked photoresist to extreme ultraviolet radiation. 3 0. A method comprising: developing the irradiated photoresist; and exposing the photoresist to an electric field while developing the irradiated photoresist -16- 200525304 (4) 3 1 The method of item 30 includes causing the photoresist development rate to be higher at the bottom of the photoresist than at the top. 3 2 · The method of claim 30, including applying an AC potential to the photoresist. 3 3 · The method of claim 30, including applying a DC potential to the photoresist. 3 4 · A semiconductor structure comprising: a substrate having a plane; a photoresist on the substrate; and aggregates interspersed in the photoresist, the aggregates being substantially laterally aligned with the plane of the substrate. 35. The structure according to item 34 of the scope of patent application, wherein the photoresist is a hydrogen-bonded polymer or a hetero-molecular polymer. 36. The structure according to item 34 of the scope of patent application, wherein the substrate is a wafer. 37. A semiconductor structure comprising: a substrate; a photoresist covering the substrate; and a water-soluble conductive layer formed on the photoresist, the conductive layer applying an electric field to the photoresist. 38. The semiconductor structure according to claim 37, wherein the conductive layer comprises a functional polythiophene polymer. 39. The semiconductor structure according to item 38 of the patent application, wherein the conductive layer comprises a functional polythiophene polymer and a sulfonate. 40. The semiconductor structure according to item 37 of the application, wherein the conductive layer includes a functional polythiophene polymer and an ammonium sulfonate. -18-